Heavy duty shear

ABSTRACT

A shear comprising a frame, a fixed blade, a movable blade cooperating with the fixed blade to cut sheet material disposed therebetween, a hydraulic power cylinder for moving the movable blade upwardly and downwardly past the fixed blade, a lever for drivingly connecting the power cylinder to the movable blade, the lever being pivotally mounted upon the frame to provide oppositely extending lever portions, one pivotally connected to the movable blade and the other pivotally connected to the ram of the power cylinder, a roller journal mounted upon brackets to extend across the frame with the brackets selectively adjustably movable to position the roller, and springs for yieldably urging the movable blade against the roller. The power cylinder is controlled by a linkage and lever mechanism which moves the control member of a valve in response to the movement of a foot pedal as well as the movement of the lever which drivingly connects the power cylinder to the movable blade.

The present invention relates to shears, and more particularly to theprovision of a heavy-duty shear for cutting relatively thick sheetsteel. Many inventors have proposed shears for cutting thick sheetsteel, and U.S. Pat. Nos. 2,645,287; 3,074,304; 3,183,756; 3,211,037;3,218,902; 3,242,786; 3,316,791; 3,371,569; 3,495,489; 3,524,374;3,530,761; and 3,691,890 are representative patents showing such priorart shear mechanisms. Reference is made to these prior art patents andthe patent references cited therein, U.S. Pat. No. 3,691,890 being myown patent.

Shears conventionally include a fixed knife blade and a verticallymovable knife blade which cooperates with the fixed knife blade to shearmaterial disposed therebetween. The fixed knife blade conventionallyprovides a horizontally extending knife edge while the movable knifeblade conventionally provides an inclined knife edge which moves pastthe fixed knife edge.

Conventionally, the movable knife blade is supported for reciprocatorymovement upwardly and downwardly by means of gibs, quides and the like.Several of the prior art patents listed above shown such conventionalgib or guide structures.

Since the lateral spacing or clearance between the fixed knife blade andthe movable knife blade must be selectively adjusted to accommodatesheet materials of different thicknesses, some sort of mechanism, andconventionally a complicated mechanism, must be provided to shift theguides for the movable blade in order to shift the movable bladerelative to the fixed blade. The Berns et al. U.S. Pat. No. 3,218,902listed above does disclose means for adjusting the clearance between themovable blade and the fixed blade, such means including springs whichurge the carrier block for the movable blade against a gib and cottersystem, the gib and cotter system being mechanically adjustable by amotor to determine the position of the block or movable blade relativeto the fixed blade.

The Giordano U.S. Pat. No. 3,242,786 listed above shows a structure bywhich the movable knife carrier block moves against a roller, theposition of which is determined by adjusting a cam acting against a camsurface on the arm which supports the roller. The carrier block isspring urged against the roller by spring washers. Then, the Pearson etal. U.S. Pat. No. 3,317,569 listed above discloses a structure includingadjustable rollers against which the carrier block for the movable bladeis urged by means of springs.

My present invention is an improvement over such prior art shear systemsbecause I pivotally mount my movable blade, or the block which supportsthe actual movable cutting blade, upon one end of a lever frame, theother end of which is pivotally connected to one or more rams ofhydraulic power cylinders. In other words, my movable blade is pivotallysuspended from one end of a crank or lever which supports as well asdrives the blade downwardly and upwardly. In order to establish thedesired clearance between the fixed blade and movable blade, I usesprings to hold the movable blade support block against selectivelyadjustable roller means, i.e., roller means journalled about an axiswhich is selectively adjustably movable relative to the fixed bladecutting edge. Then, since the adjustment of the roller means againstwhich the blade support block is urged will change the alignment of themovable blade relative to the fixed blade, my preferred pivotalconnection between the movable blade and the drive lever is a connectionwhich will permit that pivot axis to be selectively adjustably movedtoward and away from the drive lever pivot axis. As will be morecompletely described hereinafter, I prefer to use an eccentric sleevearrangement providing the selectively adjustable pivotal connectionbetween the movable blade and the drive lever.

By using such a drive lever, I can obtain a very significant mechanicaladvantage by having the lever portion connected to the drive rams longerthan the lever portion supporting the movable blade.

It is an object of my present invention, therefore, to provide such ashear wherein the improvement comprises means for guiding the movableblade means for movement past the fixed blade means, the guiding meansincluding bracket means mounted on the shear frame for selectivelyadjustable movement relative to the fixed blade means, roller meansjournal mounted upon the bracket means for rotation about an axisgenerally perpendicular to the direction of movement of the movableblade means, and means for yieldably urging the movable blade meansagainst the said roller means.

It is another object of my present invention to provide such a shearwherein the improvement comprises means for connecting the movable bladeto the power cylinder ram, the connecting means including lever meansmounted on the shear frame for pivotal movement about an axis generallyparallel to the journal axis of the said roller means and providingoppositely extending lever portions, means for pivotally connecting themovable blade means to one of said lever portions and means forpivotally connecting the ram to the other of said lever portions.

Still another object of my present invention is to provide such a shearwherein the improvement includes a bearing block supporting the movableblade means and selectively adjustable trunnion means for pivotallymounting the bearing block on the said one lever portion such that thepivot axis provided by said bearing block is selectively adjustablerelative to the pivot axis of the drive lever.

My preferred shear includes a very simple and conventional fluid valvehaving a movable valve control member with an extended positionpermitting fluid flow to extend the ram of the power cylinder to drivethe movable blade means downwardly past the fixed blade means, aretracted position permitting fluid flow to retract the ram, and aneutral position between the extended and retracted positions permittingcirculation of the hydraulic fluid without moving the drive ram. Byusing that simple and conventional control valve and a lever and linkagearrangement, I can control the movement of the movable blade very simplyby operation of a foot pedal and without the usual hydraulic limitswitches, switch-over valves, and the like.

Other objects and features of my present invention will become apparentas this description progresses.

To the accomplishment of the above and related objects, this inventionmay be embodied in the form illustrated in the accompanying drawings,attention being called to the fact, however, that the drawings areillustrative only, and that change may be made in the specificconstruction illustrated and described, so long as the scope of theappended claims is not violated.

In the drawings:

FIG. 1 is an end view of my shear;

FIG. 2 is an end view with the end plate removed and showing, insection, the major components of my shear;

FIG. 3 is a plan view of my shear;

FIG. 4 is a fragmentary sectional view showing how my movable blade isguided and supported;

FIGS. 5 and 6 are diagrammatical views showing how the movable blade isaligned relative to the fixed blade; and

FIGS. 7, 8, 9 and 10 are diagrammatical views showing how I control thepower cylinders which drive the movable blade downwardly.

Referring now particularly to the drawings, it will be seen that theshear 10 comprises a frame 12 including a pair of upstanding side plates14, 16 and a bed plate 18 extending therebetween to provide anupwardly-facing, horizontally extending work surface for receiving sheetmaterial. As best viewed in FIG. 2, the bed plate 18 is part of astructure including a vertically extending blade support member 20 and astrengthening angle plate 22. The frame structure including the sideplates 14, 16, bed plate 18, blade support member 20 and strengtheningmember 22 may be welded or otherwise securely fastened together toprovide a structurally sound shear frame. A fixed blade 22 is mountedupon the member 20 to extend horizontally along the upper edge thereoffrom side plate 14 to side plate 16. This blade 22 is held securely bymeans such as the illustrated screws 24. The cutting edge of this blade22 is generally flush with and defines the rearward edge of the worksurface provided primarily by the bed plate 18. The shear 10 may bemounted upon foot plates 26 as illustrated.

A shear must have at least one movable blade, and my shear 10 includes amovable blade 30 which is rigidly fastened by means such as illustratedscrews 32 to a blade support block 34. While it is not shown in thedrawings, it will be well understood by those familiar with the art ofshearing metal that the movable blade 30 will be inclined relative tothe fixed blade 22 such that the cutting action between the two bladestakes place at a theoretical point which moves horizontally along thecutting edge of the fixed blade 22 as the movable blade 30 movesdownwardly past the fixed blade. This relationship, of course,concentrates the force of the cutting action at a point which movesalong the material to be cut.

In the illustrative embodiment, plates 36 and 38 are mounted upon thesupport block 30 at the lower portion thereof by means such as theillustrated screws 40. It will be appreciated that the block 34 andplates 36, 38 may be integrally formed by casting or welding processes.For that reason, the whole structure comprising the block 34 and plates36, 38 may be considered a blade-support block. The blade support block34 is supported by bearing blocks 42 such that the block 34 is pivotallymovable about a horizontally extending axis generally parallel to thecutting edge of the fixed blade 22. Then, I provide brackets 46, 48mounted respectively on the side plates 14, 16 for pivotal movementabout a trunnion 50, the axis of which is horizontally extending andgenerally parallel, for instance, to the cutting edge of the fixed blade22. I provide roller means indicated generally at 54 journal mountedupon the brackets 46, 48 for rotation about a horizontally extendingaxis generally parallel to the axis of the trunnion 50. The roller means54 may include a hardened steel roller 58 mounted upon a trunnion 60extending between the brackets 46, 48. I use a spring or springs 64yieldably to urge the plate 38 against the roller means 54, theillustrative spring 64 being connected between a connection point 66 onthe plate 36 and a connection point 68 on the frame. Thus, as the block34 and plate 38 move upwardly and downwardly, the path of movement willbe controlled by the position of the roller means 54 against which theplate 38 is held by the spring 64. The journal axis of the roller means54 is selectively adjustably positioned by positioning the brackets 46,48 about the trunnion 50. As illustrated in the accompanying drawings,the journal axis of the roller means 54 is generally parallel to and atthe same general horizontal height as the fixed blade 22 cutting edge.Since the trunnion 50 is above and vertically spaced apart from theroller means 54 by a considerable distance, the journal axis of theroller means will remain at generally the same height as the cuttingedge of the fixed blade in the various adjusted positions of the rollermeans. In the illustrative embodiment, this is accomplished by havingeach bracket 46, 48 formed to include a forwardly projecting adjustmentportion 70 which is threadedly engaged by upper and lower adjustmentscrews 72, 74 cooperating with upper and lower adjustment blocks 76, 78securely mounted to the shear frame.

Thus, the distance between the cutting edge of the fixed blade 22 andthe cutting edge of the movable blade 30 is selectively adjustablydetermined by positioning the roller means 54 against which the plate 38is held. By moving the adjustment portions 70 downwardly, the axis ofthe roller means 54 is moved rearwardly relative to the fixed blade 22to widen the space between the cutting edge of the fixed blade and thecutting edge of the movable blade.

My shear 10 may include one or two or even more power cylinders formoving the movable blade, the illustrative shear having two suchhydraulig power cylinders 82, each of which provides an upwardlyextending ram 84 as a driver. Each side plate 14, 16 carries a bracket86 and the adjacent power cylinder is pivotally mounted on that bracketas indicated at 88. Then, in order drivingly to connect the powercylinders 82 to the movable blade 30, I provide a lever means or a leverframe mounted upon the upper portions of the side plates 14, 16 forpivotal movement about a horizontally extending axis generally parallelto the axis of the trunnion 50. The illustrative lever frame includesside members 92, 94 which are rigidly connected together by means of apipe section 96, gusset plates 98 and a rear pipe section 100. It willbe appreciated that these members 92, 94, 96, 98, 100 may be welded orotherwise securely fastened together to provide a rigid frame having aforwardly extending lever arm portion and a rearwardly extending leverarm portion. A trunnion 106 about which the lever frame pivots isprovided and bearing blocks 108, 110 are mounted upon the lever frame topivot upon the trunnion 106 in the illustrative embodiment. I showmounting plates 112, 114, respectively upon the side plates 14, 16 formounting and positioning the trunnion 106. It will be appreciated that anumber of different techniques may be used pivotally to mount the leverframe upon the side plates 14. 16.

In the view of FIG. 4, I designate one end or one lever arm portion ofthe lever frame by the reference numeral 118 and the opposite end by thereference numeral 120. Each ram 84 may be connected to the adjacent end120 of the lever frame by means of a bearing block 122 and trunnion 124as illustrated.

The bearing blocks 42 mentioned previously serve pivotally to connectthe blade support block 34 to the forwardly extending lever arm portions118 of the lever frame. The illustrative pivotal connection is providedby a trunnion 130 which extends between the portions 118 of the members92, 94 and which may be secured thereon by means such as theillustrative side plates 132, 134. An eccentric sleeve 136 havinginternal and external cylindrical surfaces formed respectively aboutparallel spaced apart axes is mounted on the trunnion 130 adjacent eachframe arm 92, 94. Each bearing block 42 provides a cylindrical borewhich is mounted upon the external surface of the adjacent eccentricsleeve 136. This arrangement constitutes selectively adjustable meansfor moving the axis of the pivotal connection between the blade supportblock 34 and the lever frame toward and away from the pivot axis of thelever frame. The purpose of this adjustable movement is to correct themisalignment between the fixed blade 22 and the movable blade 30 causedby shifting the axis of the roller means 54. The bearing blocks 42 areconventionally split and can be loosened by loosening the illustrativebolts and nuts 138, 140 such that the eccentric sleeve 136 can berotated about the axis of the trunnion 130. FIG. 6 shows themisalignment which would be produced by moving the axis of the rollermeans 54 toward the fixed blade 22. This misalignment is corrected byadjusting the eccentric sleeve 136 to move the axis of the bearingblocks 42 forwardly or away from the pivot axis of the lever frame.

Turning now to FIGS. 1 and 7-10, it will be seen that I have illustrateda control means for the power cylinders 82 which, as indicated above,are conventional two-direction hydraulic cylinders. The control meansincludes a conventional hydraulic valve 148 having a movable valvemember 150 having an extended position permitting fluid flow to extendthe rams 84 upwardly to move the movable blade downwardly past the fixedblade, a retracted position permitting fluid flow to retract the rams,and a neutral position between the said extended and retracted positionwhich permits circulation of the hydraulic fluid without movement of therams 84. In FIGS. 7-10, I show the valve 148 having an input line 149and three output lines 149a, 149b, 149c. In the neutral position,hydraulic fluid flows in the input line 149 and out the output line 149cmerely to be circulated without moving the rams. The neutral position ofthe valve member 150 is shown in FIGS. 7 and 9. In the extended positionof the valve member 150, fluid flows in the line 149 and out the line149a to the cylinders to project the rams 84. Such a position of thevalve member 150 is shown in FIG. 8. Then, in the retracted position ofthe value member 150, such as shown in FIG. 10, hydraulic fluid flowsinto the line 149 and out through the line 149b to the power cylindersto retract the rams 84.

In the illustrative embodiment, I use a foot pedal lever 152 pivoted onthe frame as indicated at 154 and providing a bar 156 which the operatorof the shear can push downwardly with his foot. A spring 158 will returnthe lever 152 when the operator moves his foot. Then, in order to sensethe position of the lever frame drivingly connecting the power cylindersto the movable blade, I provide a control rod 160 pivotally connected toa bracket 162 on the frame arm 92 as indicated at 164. This control rod160 may be adjusted by means of a take-up device indicated generally at166 near the fulcrum point 164. This control rod 160 cooperates with amain lever 170 pivotally mounted upon the side plate 14 for pivotalmovement about a trunnion indicated at 172. The main lever 170 providesa first arm portion 176 extending generally forwardly and a second armportion 178 extending generally rearwardly. A concentric flange 182 ismounted upon the trunnion 172 to serve as a guide for the control rod160 confining the control rod for movement adjacent the second armportion 178. Control rod 160 has an enlarged portion 184 providing upperand lower control surfaces 186, 188 between which extends a guidesurface 190. Then a block 192 is welded or otherwise securely fastenedupon the second arm portion as illustrated, and a pair of support arms194, 196 are pivotally connected to the block 192 as indicated at 198,200 to extend toward the enlarged portion 184. Stop blocks 202, 204prevent the arms 194, 196 from moving toward each other. A tensionspring 206 yieldably resists movement of the arms 194, 196 away fromeach other. Each arm 194, 196 carries a roller 208, 210 journal mountedon the distal end thereof in position to engage rollably the guidesurface 190 and the control surfaces 186, 188. I provide an intermediatelever 212 having one end portion 214 pivotally connected to the firstarm portion 176 of the main lever 170, its intermediate portionpivotally connected to the valve member 150 by a link indicated at 216,and its opposite end portion 218 pivotally connected to the pedal lever152 by a link indicated at 220. The pedal lever 152 is movable between apair of stop blocks 222, 224 as illustrated.

FIGS. 7 and 9 show the valve member 150 in neutral position with thehydraulic fluid circulating so as not to move the rams 84 in eitherdirection. When the pedal lever 152 is pushed downwardly from itsposition shown in FIG. 7 to its position shown in FIG. 8, the valvemember 150 moves to its extended position so that fluid flow to thehydraulic cylinders will cause the rams 84 to move upwardly. Thismovement of the rams upwardly will move the control rod 160 upwardly sothat the roller 210 will roll off the guide surface 190 onto the controlsurface 188, thereby to permit the main lever 170 to pivot clockwise asshown in FIG. 9 to move the valve member 150 upwardly to its neutralposition. The valve member 150 will stay in its neutral position as longas the shear operator holds the lever 152 in its lower position. Whenthe operator releases the lever 152, the spring 158 will being the lever152 upwardly to raise the intermediate lever 212 to move the valvemember 150 to its retracted position causing hydraulic fluid flow toretract the rams 84 which will lower the control rod 160 back to itsstarting position.

FIG. 7, therefore, shows the roller 208 released when the movable knifeis in its uppermost position and the valve 148 is in its neutralcondition permitting circulation of the hydraulic fluid without movingthe rams 84. FIG. 8 shows the machine in its downstroke cycling positionwith the foot pedal down and the valve member 150 in its extendedposition to allow hydraulic fluid flow to the cylinder to project therams 84 upwardly to bring the movable blade cycling downwardly and tolift the control bar 160 until it releases the roller 210. Thatreleasing of the roller 210 permits the main lever 170 to swingclockwise and push the valve member 150 back into its neutral positionagain as shown in FIG. 9. FIG. 10 shows the mechanism in the returnposition.

By the linkage and lever mechanism illustrated and just described, Ihave provided a control system which uses a very simple and inexpensivevalve 148 as the only hydraulic control valve for controlling the entireshear 10. The linkage and lever mechanism illustrated and describedeliminates any expensive and complicated hydraulic control system andcomponents such as limit switches, switch-over valves, and the like. Thestarting and stopping positions for the movable blade may be controlledvery simply, for instance, by adjusting the control rod 160 as indicatedat 166 to determine exactly when the main lever 170 will be permitted topivot to change the position of the valve member 150.

I claim:
 1. A shear including a frame, fixed blade means mounted on saidframe movable blade means cooperating with said fixed blade means to cutsheet material disposed therebetween, power means for moving saidmovable blade means upwardly and downwardly past said fixed blade means,and means for connecting said power means to said movable blade means,wherein the improvement comprises means for guiding said movable blademeans for such movement past said fixed blade means, said guiding meansincluding bracket means mounted on said frame for selectively adjustablemovement relative to said fixed blade means, roller means journalmounted upon said bracket means for rotation about an axis generallyperpendicular to the direction of movement of said movable blade means,and means for yieldably urging said movable blade means against saidroller means, said power means including a power cylinder having a ramas a driver, and said connecting means including lever means mounted onsaid frame for pivotal movement about an axis generally parallel to thejournal axis of said roller means and providing oppositely extendinglever portions, means for pivotally connecting said movable blade meansto one of said lever portions and means for pivotally connecting saidram to the other of said lever portions, said means for pivotallyconnecting said movable blade means to said one lever portion includinga bearing block supporting said movable blade means, said bearing blockproviding a cylindrical bore parallel to the pivot axis of said lever, acylindrical trunnion mounted upon said one lever portion parallel tosaid pivot axis and extending through said bore, and an eccentric sleevehaving internal and external cylindrical surfaces formed respectivelyabout parallel spaced apart axes, the internal surface of said sleevereceiving said trunnion and the external surface of said sleeve beingreceived in said cylindrical bore, whereby the position of said bearingblock relative to the pivot axis of said lever is determined by therotational position of said eccentric sleeve on said trunnion.
 2. Ashear including a frame, fixed blade means mounted on said frame,movable blade means cooperating with said fixed blade means to cut sheetmaterial disposed therebetween, power means for moving said movableblade means upwardly and downwardly past said fixed blade means, andmeans for connecting said power means to said movable blade means,wherein the improvement comprises means for guiding said movable blademeans for such movement past said fixed blade means, said guiding meansincluding bracket means mounted on said frame for selectively adjustablemovement relative to said fixed blade means, roller means journalmounted upon said bracket means for rotation about an axis generallyperpendicular to the direction of movement of said movable blade means,and means for yieldably urging said movable blade means against saidroller means, said power means including a power cylinder having a ramas a driver, and said connecting means including lever means mounted onsaid frame for pivotal movement about an axis generally parallel to thejournal axis of said roller means and providing oppositely extendinglever portions, means for pivotally connecting said movable blade meansto one of said lever portions and means for pivotally connecting saidram to the other of said lever portions, said means for pivotallyconnecting said movable blade means to said one lever portion includinga bearing block supporting said movable blade means, and selectivelyadjustable trunnion means for pivotally mounting said bearing block onsaid one lever portion, whereby the pivot axis provided by said bearingblock is selectively adjustable relative to the pivot axis of saidlever.
 3. The improvement of claim 2 in which said trunnion meansincludes a trunnion carried by said one lever portion and an eccentricsleeve mounted on said trunnion, said bearing block being mounted onsaid sleeve.
 4. The improvement of claim 3 in which said movable blademeans includes a support block suspended from said bearing block and ablade carried by said support block, said urging means including springmeans for urging said support block against said roller means.
 5. Theimprovement of claim 4 in which said bracket means includes a pair ofaxially spaced apart brackets mounted on said frame for pivotal movementabout a common axis parallel to and spaced apart from the journal axisfor said roller means, each of said brackets having a rigid adjustmentportion extending away from said common pivot axis, and means on saidframe for selectively adjustably moving said adjustment portionsselectively to position said roller relative to said fixed blade means.6. The improvement of claim 5 in which said means for pivotallyconnecting said movable blade means to said one lever portion includes abearing block supporting said movable blade means, and selectivelyadjustable trunnion means for pivotally mounting said bearing block onsaid one lever portion, whereby the pivot axis provided by said bearingblock is selectively adjustable relative to the pivot axis of saidlever.
 7. The improvement of claim 6 in which said roller means includesan axially elongated roller extending between said brackets, said springmeans including at least one tension spring connected between said frameand said support block.
 8. A shear including an upright frame providinga generally horizontal bed for holding sheet stock, a pair of sideplates extending upwardly from opposite sides of said bed, said beddefining a straight edge extending between said side plates, a fixedblade extending between said side plates and along said edge of saidbed, a movable blade extending between said side plates and cooperatingwith said fixed blade to cut sheet stock disposed on said bed andextending over said fixed blade, power means for moving said movableblade upwardly and downwardly past said fixed blade, and means forconnecting said power means to said movable blade, wherein theimprovement comprises means for guiding said movable blade for movementpast said fixed blade, said guiding means comprising brackets mountedrespectively on said side plates for pivotal movement about a commonhorizontal axis, means for selectively adjustably positioning saidbrackets, roller means journal mounted on said brackets for rotationabout an axis parallel to said common horizontal axis, a blocksupporting said movable blade, and means for yieldably urging said blockagainst said roller means, said power means including at least one powercylinder mounted on said frame to provide an upwardly extending ram as adriver, and said connecting means including a lever mounted upon saidframe for pivotal movement about an axis extending between the upperportions of said side plates and generally parallel to said commonhorizontal axis, said lever providing oppositely extending leverportions, means for pivotally connecting said block to one of said leverportions and means for pivotally connecting said ram to the other ofsaid lever portions, said means for pivotally connecting said block tosaid one lever portion including selectively adjustable means forshifting the pivot axis of said block toward and away from the pivotaxis of said lever.
 9. A shear including a frame, fixed blade meansmounted on said frame, movable blade means cooperating with said fixedblade means to cut sheet material disposed therebetween, power means formoving said movable blade means upwardly and downwardly past said fixedblade means, and means for connecting said power means to said movableblade means, wherein the improvement comprises means for guiding saidmovable blade means for such movement past said fixed blade means, saidguiding means including bracket means mounted on said frame forselectively adjustable movement relative to said fixed blade means,roller means journal mounted upon said bracket means for rotation aboutan axis generally perpendicular to the direction of movement of saidmovable blade means, and means for yieldably urging said movable blademeans against said roller means, said power means including a powercylinder having a ram as a driver, and said connecting means includinglever means mounted on said frame for pivotal movement about an axisgenerally parallel to the journal axis of said roller means andproviding oppositely extending lever portions, means for pivotallyconnecting said movable blade means to one of said lever portions andmeans for pivotally connecting said ram to the other of said leverportions, said means for pivotally connecting said movable blade meansto said one lever portion including selectively adjustable means forshifting the pivot axis of said blade means toward and away from thepivot axis of said lever.
 10. A shear including an upright frameproviding a generally horizontal bed for holding sheet stock, a pair ofside plates extending upwardly from opposite sides of said bed, said beddefining a straight edge extending between said side plates, a fixedblade extending between said side plates and along said edge of saidbed, a movable blade extending between said side plates and cooperatingwith said fixed blade to cut sheet stock disposed on said bed andextending over said fixed blade, power means for moving said movableblade upwardly and downwardly past said fixed blade, and means forconnecting said power means to said movable blade, wherein theimprovement comprises means for guiding said movable blade for movementpast said fixed blade, said guiding means comprising brackets mountedrespectively on said side plates for pivotal movement about a commonhorizontal axis, means for selectively adjustably positioning saidbrackets, roller means journal mounted on said brackets for rotationabout an axis parallel to said common horizontal axis, a blocksupporting said movable blade, and means for yieldably urging said blockagainst said roller means, said power means including at least one powercylinder mounted on said frame to provide an upwardly extending ram as adriver, and said connecting means including a lever mounted upon saidframe for pivotal movement about an axis extending between the upperportions of said side plates and generally parallel to said commonhorizontal axis, said lever providing oppositely extending leverportions, means for pivotally connecting said block to one of said leverportions and means for pivotally connecting said ram to the other ofsaid lever portions, said means for pivotally connecting saidblade-supporting block to said one lever portion including a bearingblock supporting said block and providing a cylindrical bore, a trunnionmounted upon said one lever portion to extend through said bore, and aneccentric sleeve mounted upon said trunnion, said bearing block engagingthe outer surface of said eccentric sleeve whereby the position of saidbearing block relative to the pivot axis of said lever is determined bythe rotational position of said eccentric sleeve on said trunnion.
 11. Ashear including an upright frame providing a generally horizontal bedfor holding sheet stock, a pair of side plates extending upwardly fromopposite sides of said bed, said bed defining a straight edge extendingbetween said side plates, a fixed blade extending between said sideplates and along said edge of said bed, a movable blade extendingbetween said side plates and cooperating with said fixed blade to cutsheet stock disposed on said bed and extending over said fixed blade,power means for moving said movable blade upwardly and downwardly pastsaid fixed blade, and means for connecting said power means to saidmovable blade, wherein the improvement comprises means for guiding saidmovable blade for movement past said fixed blade, said guiding meanscomprising brackets mounted respectively on said side plates for pivotalmovement about a common horizontal axis, means for selectivelyadjustably positioning said brackets, roller means journal mounted onsaid brackets for rotation about an axis parallel to said commonhorizontal axis, a block supporting said movable blade, and means foryieldably urging said block against said roller means, said power meansincluding at least one power cylinder mounted on said frame to providean upwardly extending ram as a driver, and said connecting meansincluding a lever mounted upon said frame for pivotal movement about anaxis extending between the upper portions of said side plates andgenerally parallel to said common horizontal axis, said lever providingoppositely extending lever portions, means for pivotally connecting saidblock to one of said lever portions and means for pivotally connectingsaid ram to the other of said lever portions, said means for pivotallyconnecting said blade-supporting block to said one lever portionincluding a bearing block carrying said blade-supporting block, saidbearing block providing a cylindrical bore parallel to the pivot axis ofsaid lever, a cylindrical trunnion mounted upon said one lever portionparallel to said pivot axis and extending through said bore, and aneccentric sleeve having internal and external cylindrical surfacesformed respectively about parallel spaced apart axes, the internalsurface of said sleeve receiving said trunnion and the external surfaceof said sleeve being received in said cylindrical bore, whereby theposition of said bearing block relative to the pivot axis of said leveris determined by the rotational position of said eccentric sleeve onsaid trunnion.
 12. A shear including a frame, fixed blade means mountedon said frame, movable blade means cooperating with said fixed blademeans to cut sheet material disposed therebetween, power means formoving said movable blade means upwardly and downwardly past said fixedblade means, and means for connecting said power means to said movableblade means, wherein the improvement comprises means for guiding saidmovable blade means for such movement past said fixed blade means, saidguiding means including bracket means mounted on said frame forselectively adjustable movement relative to said fixed blade means,roller means journal mounted upon said bracket means for rotation aboutan axis generally perpendicular to the direction of movement of saidmovable blade means, and means for yieldably urging said movable blademeans against said roller means, said power means including a powercylinder having a ram as a driver, and said connecting means includinglever means mounted on said frame for pivotal movement about an axisgenerally parallel to the journal axis of said roller means andproviding oppositely extending lever portions, means for pivotallyconnecting said movable blade means to one of said lever portions andmeans for pivotally connecting said ram to the other of said leverportions, and means for controlling said power cylinder, said controlmeans comprising a fluid valve having a movable valve control memberwith an extended position permitting fluid flow to extend said ramupwardly to move said movable blade means downwardly past said fixedblade means, a retracted position permitting fluid flow to retract saidram, and a neutral position between said extended and retractedpositions, a main lever pivotally mounted upon said frame and providingfirst and second oppositely extending arm portions, a spring-returnedfoot pedal, an intermediate lever having one end pivotally connected tosaid first arm portion, an intermediate portion pivotally connected tosaid valve control member, and an opposite end pivotally connected tosaid foot pedal, means for controlling the pivotal movement of said mainlever, said movement control means including a control rod pivotallyconnected to said other lever portion of said first named lever means,said control rod extending to intersect said second arm portion of saidmain lever, said control rod providing, adjacent said second armportion, an enlarged portion having oppositely facing control surfacestransverse to the direction of extension of said control rod and,extending between said control surfaces, a guide surface, a pair of armsmounted upon said second arm portion for pivotal movement about axesparallel to the pivot axis for said main lever, each of said armscarrying, at its distal end, a roller rollably engaging said guidesurface and the adjacent control surface, said rollers being effective,when both are engaging said guide surface, to prevent pivoting of saidmain lever, spring means for yieldably resisting separation of saidarms, and stop means for preventing said arms from moving toward eachother, said control rod being movable with said first named lever meansrelative to said second arm portion such that said main lever can pivotabout its axis when one of said rollers moves from said guide surfaceonto one of said control surfaces.